Stoker damper control



' Oct. 17, 1944. c. HOTCHKISS STOKER DAMPER CONTROL Filed Aug. 3, 1940 2 Sheets-Sheet 1 Oct. 17, 1944. C flo c K ss 2,360,347

STOKER DAMPER CONTROL Filed Aug. 3, 1940 2 Sheets-Sheet 2 BY fifw ATTORNEY.

Patented Oct. 17, 1944 S'TOKER DAMPER CONTROL Clifford Hotchkiss, Milwaukee, Wis., assignor to Perfex Corporation, Milwaukee, Wis., a corporation of Wisconsin Application August 3, 1940, Serial No. 350,715

16 Claims.

This invention relates in general to damper controls for stoker operated furnaces. and more particularly to an improved damper control for automatically regulating the amount of combustion air delivered to the furnace retort.

The principal object of the invention is to provide automatic means for maintaining a proper ratio between the fuel being burned in a furnace and the draft or combustion air supplied thereto under varying operating conditions whereby the furnace is operated at its maximum efficiency at all times.

In the operation of furnaces equipped with stoker fuel feeding means it is customary to provide an air fan operated at constant speed by the stoker motor to deliver forced combustion air to the furnace retort. This forced air is delivered simultaneously with the feeding of fuel to the retort in order to promote'good combustion of the fuel. In domestic installations the stoker apparatus is usually operated automatically by some temperature control device such as a room thermostat when the temperature of a room falls to a predetermined minimum value, and stopped upon the temperature reaching a higher value. There is also usually provided an interval timer device for operating the stoker apparatus periodically independent of the room thermostat so that the fire will be maintained alive during long periods when the room thermostat is not calling for heat. During continued operation of the fuel feeding mechanism to feed coal upon the furnace retort, the portion of the fuel bed through which the combustion air is forced is maintained at a fairly consistent depth and density when the rate of fuel feeding is substantially equal to the rate of burning. However, during an off or stand-by period of the stoker the fuel upon the retort continues to burn as a result of some natural draft, and the thickness or resistance of the fuel bed may be substantially reduced before the next operation of the stoker occurs. Hence when the stoker is started again the initial blast of forced combustion air from the fan will blow the fine or fly ash through the thin fuel bed before the bed can be built up with green coal. Blow holes may also occur in the thin fuel bed through which the forced air will rush and rapidly burn out the fire faster than the coal can be fed to the retort by the stoker. Likewise when the Stoker has been operating periodically for relatively long periods under control of an interval timer or other type of fire maintaining means and the fire bed is low or thin or the coal has become coked, then starting the stoker with a full blast of air from the fan may tend to unduly cool off the fire or even blow it out.

The depth or thickness of a fuel bed upon the furnace retort, and therefore the porosity or resistance of the same through which the combustion air must be forced in order to reach the burning fuel is accordingly a measure of the efficiency at which the furnace is operating. For xample if the combustion air is delivered to the fuel bed retort at substantially a constant volume and pressure, a greater volume of air will pass through a thin fuel bed than the volumetric rate will be through a thick fuel bed whose resistance is high, resulting in the blowing of fly ash as pointed out. Conversely with a thick fuel bed considerable resistance may be developed against the forced combustion air and the burning fuel will receive a deficiency of air, resulting in a reduced rate of combustion and also a further increase in the thickness of the fuel bed as the stoker continues to operate. In addition, if the forced air is at such a pressure and .passes through the fuel bed at a rate to produce a pressure above the fuel bed in the combustion chamber, some smoke may be forced back through the fuel feeding screw to the room in which the stoker is located.

The resistance of the fuel bed to the forced air also may not remain constant or uniform even if the rate of air supply and coal is maintained constant. This may be due to the tendency of the coal to coke, the accumulation of fine green coal over the tuyeres, or an accumulation of ash and clinkers may increase the resistance. A decrease in the resistance of the fuel bed may also occur due to the shrinkage of coke away from the tuyres, a temporary supply of coarse coal,

or an unusual rate of combustion during a standby period due to natural draft. The above changes in fuel bed resistance will mean a change in the rate of delivery of the forced air by the fan. These changes it will be perceived will ocour in the direction tending to aggravate the cause of the disturbance. For example, if the resistance of the fuel bed increases for any reason, the delivery of forced air is decreased. This decreases the rate of burning fuel which results in the thickness of the fuel bed increasing. Its resistance is thus increased and the supply of air is decreased even more.

One of the important objects of this invention is to eliminate or greatly reduce the foregoing disadvantages and substantially increase the efficiency of the operation of a furnace by providing a stoker damper control which will automatically function to maintain the rate of forced air supply constant, or increase it if the resistance of the fuel bed to the forced air increases for an reason, in order that the fuel bed may be brought back to normal combustion conditions. If the fuel bed resistance becomes low, the automatic damper control is arranged to function to maintain a uniform rate of air supply or decrease the supply until the fuel bed has been built up to normal level again by the feeding of the coal.

Another object of this invention is to provide an automatic stoker damper control in which the air damper is retarded in its initial opening operation to delay the delivery of the full blast of a,

normal air to the fuel bed until a proper amount of coal has been fed upon the fire bed, and to gradually open the damper to its full open position and permit maximum air volume only after the stoker has been in operation for a while, whereby the diffusion of fly ash throughout the furnace and stack is substantially eliminated or greatly minimized. This delay also enables the fly ash to become substantially fused and thereby prevent its diffusion.

It is a further object of the invention to provide a stoker air damper in which a delayed opening of the damper takes place responsive to the control by the room thermostat upon a call for heat, but under hold-fire conditions when the stoker is controlled by the stoker interval timer to maintain the fire alive, the damper remains in closed position. This is desirable because during the hold-fire periods the fuel bed is usually at a very low stage and the feeding of coal during this relatively short period is suificient to maintain the fire alive by natural draft until the next hold-fire period. The hold-fire periods are usually adjusted for shorter intervals than the time occupied in the delayed opening of the air damper.

A further object is to provide a novel static air pressure responsive means operated by the static pressure produced below a fuel bed for controlling a stoker air damper 7 whereby the proper fuel bed thickness for efficient firing is maintained at all times in consonance with the corresponding volume of combustion air for efficient combustion of the burning fuel.

A further object is to provide a stoker air damper control having an electrically controlled thermally actuated means for controlling the delayed opening of the air damper.

An additional object is to devise an improved stoker air damper control constituted as a single unitary structure which is adaptable for use upon various types of stoker air ducts and which maybe readily applied to existing installations without extensive alterations to the same.

With the foregoing and other objects in view, which will become mor fully apparent as the nature of the invention is understood, the invention consists in the new and novel features of construction, omration and arrangement of the parts as will be hereinafter more fully described, illustrated in the accompanying drawings, and defined in the appended claims.

The invention in one of its preferred forms is illustrated in the accompanying drawings in which:

Fig. 1 shows diagrammatically a view of a stoker furnace installation together with the various control elements and the associated electrical wiring therefor;

Fig. 2 is a top view of the damper control device of the invention;

Fig. 3 is a top view with the cover removed showing the mechanism within the control hous-- mg;

Fig. 4 is a cross-sectional side view taken along the line 4-4 of Fig, 3 and showing the air damper within the air duct;

Fig. 5 is another top view of the control de- Vice showing one stage in the operation of the same; while Fig. 6 is a fragmentar view of a modified form of the invention.

Referring now specifically to Fig. 1 a conventional stoker furnace installation is shown comprising a retort 8 for supporting the burning fuel bed within a furnace, not shown, and having the usual ash plate 9 surrounding the retort 8. The

,retort 8 is arranged with a series of tuyres or air ports II] in the sides thereof for the admission of forced combustion air to the burning fuel bed from a wind box II situated below the retort. A coal hopper l2 for the fuel supply also serves to enclose the stoker motor I3 and associated gear mechanism, not shown, for driving the fuel conveyor or screw I4 and thereby feed fuel from the hopper l2 to the retort 8. An air blower or fan I5 is shown coupled with the motor I3 and is driven by the motor to force combustion air for the burning fuel through a conduit or air duct [6 to the wind box II and the retort 8. The Volume of air for the fan I5 may be regulated by the adjustable air intake shutter I1 arranged on the side of the hopper l2. In some stoker installations separate motors for the fuel conveyor I4 and for the blower fan l5 may be preferred instead of a single motor for both as shown. I

The operating control means for operating the stoker installation includes a relay having a winding l8 adapted when energized to close the motor contacts l9 and complete an operating circuit to the windings of motor I3 from a source of suitable commercial current fed over the line wires 20 and 2!. A transformer 22 is connected across the line wires 20 and 2| and is provided with a low voltage secondary winding arranged in the circuit of relay winding I8 for energizing the same. The primary control for operating the stoker may be any type of control means whereby the stoker is operated automatically when the temperature of a room drops below a minimum value, or the steam pressure of a furnace is below the desired value. In the form preferred this may comprise a room thermostat 23 having a set of operating contacts which are closed upon a drop in temperature to complete an energizing circuit for the relay l8. During long intervals between operations of the thermostat 23 such as would occur in mild weather, it is customary to provide an interval timer to maintain the fire alive. This may take the form of an electric motor 24 to which a cam is coupled for closing a pair of contacts 25 at regular adjustable intervals and for relatively short adjustable periods of time. These contacts 25 are arranged in parallel with the contacts of the room thermostat 23 and perform the same function of controlling the stoker motor.

The foregoing control apparatus, it will be understood, is the conventional means for controlling the operation of a furnace stoker, although some variations in the form and number of controls may be desirable in different types of installations. A furnace stoker operating with the foregoing controls will operate in a somewhat satisfactory manner as long as the fuel feed and the forced air passing to the retort 8 on the burning fuel bed are in the correct proportion and ratio to provide eflicient burning-of the fuel and a consistent depth of the fuel bed. This is true also as long as all other conditions such as the type of fuel, the rate of burning, etc., as has been pointed out, are satisfactory. However, because ascoem:

of these unnatural conditions. the air and. fuel feed proportions may become unbalanced. producing; an unstable fuel bed with the disadvantages which have been enumerated, resulting. in theless' efficient and unsatisfactory operation of the stoker. It is the purpose of this invention. to obviate these difficulties with the automatic damper control which automatically provides the correct proportion of combustion air in consonance with the feeding of the fuel to the retort and the depth or resistance of the burning fuel. bed thereon. This automatic damper control is indicated in the drawings generally at 26 and is arranged on the air duct l6 in aposition between the fan and the wind box II where it can exercise full control over the volume of forced combustion air passing from the fan to; the; stoker retort.

The automatic damper control 26, as, seen more specifically in Fig. 4, includes ametal housing. or

casing 271 having angle brackets 28 secured as.

shown toeach end thereof whereby the housing: 2-! as a unit may be readily installed and mounted on top of the air duct it by means of the; screws 29 passing through the angle brackets 28. into the top of the duct. A cover 30 is, provided for the housing 21 which is removably secured there.- to by means of the screws 3|. Extending downwardly from the housing 21 and fastened tothe bottom thereof by means of a pair of screws 33; is. a supporting frame member 32 conforming gen.- erally to the inside shape of the air duct t6. and arranged to fit closely therein. This frame 32 extends into air duct [-9 through an opening cut in the top of the air duct and is arranged tosupport an air valve or damper 34 within the air duct. Since the damper support 32 issecurelyattached to the housing 21 it will be seen that the complete housing and damper support, including the damper 34, are constructed as a single unitary structure which is readily and removably attached to the air duct without extensive supporting arrangements and alterations thereto.

The air damper 34 is rigidly secured to an operating shaft 35 by means of screws 36 while the shaft 35 itself is journaled and supported in the. bottom of the supporting frame 32 by a bearing 31. For a purpose which will be hereinafter pointed out, the damper 34 is not secured to the: shaft 35 at the midpoint between the damper edges, but is secured so that a right hand portion 38 of the damper is somewhat longer than; the left hand portion as viewed in Fig. 4 and the. damper is therefore unbalanced on the. shaft. The damper is wider than the width of the air duct so that in the closed position the damper. is disposed angularly within the air duct and by engaging the sides thereof serves to provide a stop for the damper movement, and also to close off the air duct more tightly to obstruct the passage of air through the duct. The supporting frame 32 and the damper 34 comprise the only elements which are positioned within the air duct.

t6, the control means for the damper being positioned outside of the air duct where the elements cannot interfere with or obstruct the flow of forced combustion air through the air duct.

The control operating means for regulating the position of the damper 34 within the air duct i6 includes an operating or control vane 39 which is secured at one end by screws 49 to the shaft 35 for pivotal movement therewith. Since the control vane is rigidly connected to the same shaft that the air damper 34 is connected to,

; crating movements.

any movement of the control vane results in corresponding movement of the air damper. A curved partition wall 4| is secured between the side walls of housing 21. and is formed to coincide.

with the curved path of movement of the free end of the control vane 39. The control vane 39 is arranged within the housing so as to provide a very close fit around its upper and lower edges, as well as the end adjacent the partition 41, to reduce leakage to a minimum while permitting free unobstructed movement of the control vane. For the same reason the damper 34 closely conforms to the shape of the supporting bracket 32 so that very little air can pass the damper in its closed position, while still permitting free and unobstructed movement to the same. An opening 42 is provided in the bottom of housing 21 topermit the static air pressure from the retort side of the air damper 34 to communicate with the interior of housing 21. Arranged within the housing 2'! and extending from the top to the bottom sides thereof is an angular shaped partition 43 provided for the purpose of preventing the air pressure from communicating with the space at one side of the vane 39. The path over which this air pressure exerts its force is indicated by the direction of the arrows in this figure. The partition 43 is providedwith an ear portion 44 on the bottom edge whereby the same may be screwed to the bottom of'the housing 21. Another ear portion is formed on the top edge of the partition 43 and serves as a bearing for the upper end of the damper operating shaft 35. Several screws 4.6 secure the partition 43 to one side of the housing. 21.

A second partition 47 is arranged within the housing 2? and is attached to the sides thereof by means. of screws G8 at both ends of the partition. Arranged within the space provided by the partition 4'. is a slow operating device shown here in the form of an electrically operated thermally actuated member. In its preferred form this slow operating device comprises a fiat piece of bimetallic material 49 secured at one endas shown to a supporting block 59 attached to the side walls of the housing 2.7 as by screws. The opposite. end of the bimetal element 49 is arranged to be free for performing certain op- In order to thermally actuate the b-imetal blade 49 an electric heater element at is provided and arranged preferably upon the blade 49. The heating of the blade 49. by the electric heater 5i effects a warping movement of V the free end of the bimetal blade and anadjustable stop em on the partition 4'1 serves to limit the movement of the blade. A flexible member in the form of a coil spring 52 has one end connected to the movable end of the bimetal element 49 and is arranged to pass through an opening 53 in the side wall of the partition 41. The purpose of providing a partition around the slow operating device is to thermally insulate the same from the air currents passing through the opening 42 into the casing 21 and therby prevent the air from cooling off the bimetal element when it is being operated by the heater 5|.

A relatively stiff blade 54 is arranged parallel with and extends from the pivoted end of the control vane 39 to a point beyond the shaft 35. A. second blade 55 slightly longer than blade 54 but which is constructed of relatively thin flexible material, is arranged directly against the stiff blade 54. Both blades are secured together at one end by rivets. 56 to the control vane 39. The free end of flexible blade 55 is provided with an adjusting screw 51 and associated clamping nuts. This screw 51 extends through a slot 58 in blade 55 and is arranged to be slidably adjusted within the limits of the slot 58 near the free end of the blade 55 as best seen in Fig. 4. One end of the coil spring 52 is secured to the screw 51 and provides the operating connection between the free end of the bimetal blade 49 and the control vane 39. The tension of the coil spring 52 in the normal inactive position of the control device as seen in Fig. 3 is suificient to hold the control vane 39 in its damper closing position. By shifting and adjusting the screw 5'! in the slot 58, the spring rate of the coil spring 52 is readily calibrated. A second adjusting screw 59 is provided which extends through a hole in the thin blade 55 and threads through stiff blade 54. The end of the adjusting screw 59 is arranged in abutting relationship with the control vane 39 so that by adjusting the screw 59 the stiff blade 54 is moved at its free end any desired amount with respect to control vane 39 and carrying the thin blade 55 along with it. This arrangement is to provide an adjustment for the coil spring 52 by positioning the thin blade 55 so as to provide the proper tension to the coil spring 52. A third adjusting screw 50 is provided which extends through a hole in the spring blade 55 and is threaded through stiff blade 54 and clamped thereon. The purpose of this screw 69 is to limit the separation between the thin blade 55 and the stiff blade 54 by the blade 55 engaging the head of the screw 60 under certain conditions of operation. A flexible leaf spring BI is supported within the housing 21 at one side thereof by having one end clamped under the end of partition 43 by screw 46. In its extreme damper opening movement the control vane 39 engages the free end of the spring blade 6| for the purpose of steadying the operation of the control vane in this extreme position and prevent erratic operation of the vane.

The cover 30 of the damper control is provided with an opening 62 for the purpose of permitting the escape of the air from the housing 2'! which leaks around the edges of the control vane. This arrangement causes the pressure on the lower side of vane 39 as viewed in Fig. 5 to approach atmospheric pressure in spite of the leakage around the control vane. This escape port 62 is provided with an adjustable cover or bracket member 63 for regulating the size of the opening 62 to any desired amount. The bracket member 63 is arranged with an angular spaced portion 64 to permit the air to pass out of the casing 21 while preventing small objects or dirt from dropping into the opening. A screw 65 fitting in a slot in the bracket member 63 provides a means for adjusting the size of the opening and for holding the bracket to the cover. An indicating scale 66 cooperating with the right hand edge of the bracket 63, as seen in Fig. 2, provides an indication of the value of the adjusted position of the bracket 63 and the size of the opening 62.

In order to visually indicate the position of the air damper 34 at any particular time in its operation, an indicator 61 is provided on top of the cover 30 which is rigidly fastened to the upper end of the operating shaft 35 and moves therewith. The indicator 6'! is adapted to cooperate with the indicia 68 stamped on the cover 30 in values to indicate the cubic feet per minute of the air passing through the air duct and past the air damper.

In the operation of the stoker apparatus, assume that the room thermostat 23 closes its contacts upon a drop in room temperature, the relay I8 is energized from the low voltage secondary of the transformer 22 and closes its contacts [9 and thereby establishes an operating circuit for the stoker motor l3 and the electrical resistance 5| in parallel therewith, from the line conductors 20 and 2|. Due to the fact that the fuel supplied to the stoker during its last operation is partially burned by natural draft during the off or standby period, this fuel bed will be relatively thin and its air resistance low. Also at this time the damper 34 completely obstructs or closes the air duct 16 except for the small amount of seepage around the edges of the damper to provide natural draft. By reason of the tension exerted by coil spring 52 upon the control vane 39 through the medium of leaf springs 55 and 54 the damper 39 is held closed as illustrated in Fig. 3. The operation of the stoker motor [3 results in the conveyor screw l4 feeding coal from the hopper l2 through the bottom of the retort 8 to the thin burning fuel bed. The fan l5 at the same time operates to force combustion air through the duct l6, but since the damper 34 is now in its closed position very little of this forced air can pass through the duct to the tuyres ID to the burning fuel bed. This action of the fuel being fed to the fuel bed before the forced air can pass through the same prevents the blowing of fly ash throughout the furnace, serves to cause fusing of some of the fly ash, eliminates the blowing of blow holes through the thin fuel bed and prevents other disadvantages as have been pointed out. I

The fuel is fed to the retort 8 until a predetermined time period has elapsed, during which the fuel bed has been built up with green coal to a suflicient depth and desired thickness as well as resistance for efiicient firing. During this interval this fuel is also being gradually ignited by the small amount of air passing the closed damper. This elapsed time is determined by the action of the slow operating device in which the heater 5|, which is concurrently energized with the motor, begins to gradually heat up the bimetal element 49 and cause it to slowly warp in an upward direction, as viewed in Fig. 5. The movement of the free end of warp element 49 gradually releases the tension of. coil spring 52 upon the control vane 39. However, due to the building up of static pressure within the air duct between the fan and the damper and which static pressure exerts itself upon the unbalanced portion 38 of the damper with greater force because of its larger area than the portion on the opposite side of the shaft 35, the control vane is prevented from opening the damper when the bimetal element is warped to an intermediate position in which the coil spring 52 no longer exerts its influence upon the control vane 39. In other Words, the coil spring 52 is so adjusted that when the tension of the coil spring upon the control vane has been released, the static pressure built up against the unbalanced portion 38 of the damper 34 is suflicient to maintain the damper in its closed position for a short interval. The full volume and blast of air from the fan through the air duct I6 is thereby delayed for a short period from exerting itself upon the burning fuel bed. As the warp element 49 continues to move its free end a point is reached in which it functions damper 34.

the partially open damper.

to perform a compressive action upon thecoil spring 52 against the static head pressure exerted against the unbalanced portion 38 of the This compressive action upon the coil spring 52 by the warp element 49 is great enough to overcome the static pressure exerted against the damper 34 and when this occurs the coil spring exerts its effort against the end of the thin spring blade 55, forcing it away from contact with the relatively stiff blade 54 and into contact with the head of screw 60. As a result the control vane 39 is free to gradually move a limited amount to a position as indicated at 69 in Fig. 5. This permits a certain air flow to pass In this position the total air pressure against the damper and the compressive effort of coil spring 52 are approximately balanced and the control vane 39 is free to floattsolely by the slight effort exerted by the thin spring blade 55 and within the limits to which the head of adjusting screw is adjusted with respect to the blade 55. This position is clearly indicated in Fig. 5. Since the control vane 39 has rotated the damper 34 through the medium of shaft 35, to a slightly open position, a small volume of air is permitted to pass to the retort to promote combustion and enable the building 'up of static air pressure below the fuel bed as will be pointed out. The movement of the element 49 is halted by its engagement with the adjustable stop 5la at the end of the time period.

The foregoing operations may take an appreciable length of time, for example several minutes, during which the fuel is being constantly fed to the fire bed to build it'up to the required depth and thickness for efficient firing. With the damper opened to the position as has been pointed out, the air flow through the air duct I6 passes to the retort 8. Since there is no longer any danger of blowing fly ash because of the green coal fed upon the fuel bed, this forced air is efiective to promote combustion of the-burning fuel. However, since the damper is open only a slight amount the full force of the air fan !5 at this time does not exert itself upon fuel bed also enables .the loose fly ash which is not burnt to be gently urged to the outer edge of the retort-where it can subsequently be formed into a clinker when the fire gets hot enough. As the thickness of the fuel bed gradually builds up, and hence its resistance'to the passage of forced combustion air through it, static pressure is gradually built-up in the wind box I I and in the air duct connecting it with the damper 34. This static air pressure below the fuel bed builds up further as the fuel bed thickens since the rate of fuel feeding is greater than the rate of combustion of the'burning fuel bed. .After a time sufficient static pressure is built up below the fuel bed and inthe air duct so that itmanifests itself through the opening 42 in the top of the air duct l6 and thebottom of the housing 21. This static pressure exerts itself in the direction indicated by the arrows inF'ig. 3, past one side of the partition 43, to theside of the control vane 39 and some leaks out of the'escape p'ort -t2. As this static pressure builds up with the increased resistance of the thickening fuel bed, the-control vane 39 is gradually and correspondingly moved farther and farther in'a downward direction as viewed in Fig. 3, and the damper 34 is accordingly moved incremently toward open position. The increase in the opening of the cised by the control device 26.

damper permits a greater volume of combustion air to pass through the duct [-5 to the fuel bed to increase the rate of combustion of the burning fuel.

.As long as the stoker motor [3 continues to operate the fuel will be fed to the burning fuel bed and the correct amount of combustion air will be passed to the same, the correct proportion being governed solely by the control exer- Near its fully open position the control vane 39 encounters the end of the leaf spring 6| which applies a certain amount of resistance to the movement of the control vane tending to force it back to the damper closing position. This spring, however, is very light andmerely serves to guide and steady the operation of the control vane as it nears the full damper opening position and prevent erratic incremental operation of the vane. .The position of the control vane 39 in which it has fully opened the damper 34, is indicated at H in Fig. 5. 7

As the control vane 39 moves closer to full damper openingposition the coil spring 52 is graduallystretched and imposes this restraining force against the forceof the static pressure exerting itself against the control Vane so that it requires a higher staticpressure to operate the vane as the damper approaches its full open position. The leakage of air pressure around the edges of the control vane and through the escape port'6-2 enables the control vane to move more smoothly and prevent the equalization of pressures on both sides of the vane which would cause the vane to restore todamper closed position. There is always a pressure drop present between the two sides of the control vane. Er-

ratic or quick movements'of the same and therefore the damper are obviated, and an easily adjustable control over the movement of the vane is provided by means of the adjusting bracket 63.

At this point it may be pointed out that in the incremental operation of the control vane 39 the forces necessary to cause the incremental movement of the control vane must necessarily be greater upon the initial movement than the force required to move the Vane after it has neared its maximum opening position. It is for this-reason that the spring blade 55 is also provided as a coupling between the vane 39 and coil spring 52 to steady the initial incremental movements of the vane, and the spring blade 6| provided to maintain the same incremental movements of the vane near its full openingposition. Erratic operation of the vane movement is thereby avoided and a smooth incremental operation is effected.

It will be apparent from the foregoing explanation that the volumetric rate at which the forced combustionair is supplied to the burning fuel is rendered dependent upon ithe'resistance of the .fuel .bed to the passage .of air there-' properly regulate the operation of the control vane 39 in accordance with the various types of stoker installations, air ducts, and other factors, the adjusting bracket 63 may be adjusted to vary the size of the escape port 62 in the cover 30. Increasing the size of the port 62 adjusts the operation of the control vane 39 so it will operate with less static pressure and thereby more quickly open the damper as the fuel bed resistance increases. This may be desirable in the case where the type of coal being burned is highly volatile.

When the room thermostat 23 has become satisfied due to the heating up of the furnace and the passage of heat to the room in which the thermostat is located, it opens its contacts. As a result the relay I8 is de-energized and it opens its contacts i9 to stop the operation of the stoker motor 13. Accordingly the feeding of fuel to the retort is halted and the electric heater is deenergized. The warp element 49 thereby gradually cools off. As a further result of the stopping of the stoker motor the air fan I5 ceases to operate so that it no longer forces air through the air duct l5. When this occurs, the static pressure below the fuel bed in the retort 8 disappears and no longer exerts its effort against the control vane 39. As a result the control vane moves clockwise under control of the tension stored within spring 52 and moves toward damper closing position, but it does not move completely back to its normal position. The control vane, however, does stop at an intermediate position as indicated at 10 in Fig. 5. In this position it floats freely in the housing 2'! under guidance of the coil spring 52 which in this position is no longer stressed, either by compression or expansion. As the warp element 49 cools, it moves the end of coil spring 52, and gradually applies tension to the thin leaf spring '55 against the rigid blade 54, and when this occurs the control vane 39 is moved along with these elements until the vane reaches its normal position shown in Fig. 3. In this position the damper 34 is fully closed and with the warp element 49 completely cooled off, the coil spring 52 exerts a force upon the control vane 39 to tightly hold the damper in its closed position.

The slow return movement of the control vane to damper closing position permits some natural draft passing through the air duct I6 from the shutter I! to be effective for a short interval upon the fuel bed. This delay in damper closing is desirable in order to prevent smoke from passing back through the fuel conveyor housing and the air duct 16, and from passing into the stoker hopper l2 and in the room Where the stoker is located. This action also permits the volatile gases on th"'e fuel bed to be burned out of the green coal fed to the fuel bed just before the stoker was stopped and helps prevent a smoking chimney.

From the foregoing it will be seen that the coil spring 52 is utilized to perform several different functions. When the stoker is at a state of rest it is effective to hold the damper in closed position so that it acts as a banking damper. Upon the beginning of the stoker operation its tension is released and it is effective to permit the control vane to be held in damper closing position by the static pressure built up by the fan in front of the closed unbalanced damper. After the warp element is fully operated the coil spring 52 is compressed and is effective to urge the control vane in a direction to initiate the damper opening movement before the static pressure under the fire bed builds up. After this the spring acts to gradually apply a restraining force to the control vane as the damper is opened.

The bimetal element 49 and the heater 5| are located within the housing 21 and separated by the partition 41 from the path of the static air pressure in order that this air will have no effect upon the operation of the bimetal element 49 and possibly prematurely cool it'off.

In the closed position of the damper 34, sufficient air or natural draft passes around the edges of it through the air duct IE to maintain the fire alive without burning it too rapidly until the next stoker operation, accordingly in the closed position it acts as a banking damper. The amount of natural draft for the fuel bed when the stoker is at rest may be conveniently adjusted by means of the adjusting blade 12 covering the small opening in the damper 34.

During times when there are long intervals between operations of the room thermostat 23, such as would occur during mild weather, the interval timer 24 is effective to maintain the fire alive. At regular time periods, for example every half hour, the timer contacts 25 are closed for a short adjustable interval, for example less than two minutes, by the continuous operation of timer motor 24. The closure of timer contacts 25 energizes the relay l8, resulting in the operation of the stoker motor l3 and the fan I 5. The fuel conveyor [4 feeds fuel upon the fire bed which at this time may be burning at a very low rate and probably contains a high ash content by having been burned down thin from the time of the last stoker operation. The electric heater 5| for the warp element 49 is energized simultaneously with the motor l3 and begins to heat up the bimetal blade. However, before the bimetal blade can be heated and Warped to its fullest extent, the timer contacts 25 are again opened. The duration of closure of these timer contacts is preferably adjusted and arranged to be for shorter time periods than it requires the warp element 49 to be fully actuated and initiate the movement of the control vane to damper opening position. The purpose of this is that during periods of hold fire" operation it is not usually necessary to open the damper 34 in the air duct Hi to permit the delivery of forced combustion air to the retort. The time periods of the closure of timer contacts 25 and their frequency of closure are governed by the type of fuel being burned and the rate of fuel feeding, in order that proper and efiicient burning of the fuel can take place between hold-fire operations of the stoker. The small amount of air which does pass around the closed damper 34 and the slight natural draft throughout the furnace below the burning fuel bed on the retort 8, is sufficient between intervals of operation of the stoker to permit the burning of the fuel by natural draft without loss of the fire. The operation of the interval timer enables just sufficient fuel to be fed to the fire bed to maintain the fire alive until the next operation of the interval timer or until the room thermostat calls for heat. If the closure of the interval timer contacts 25 is adjusted for slightly longer intervals as may be desirable under certain conditions where the fuel is less volatile the warp element 49 is permitted to operate to a position in which the control arm 39 moves to the point indicated at 69 in Fig. 5. This is the position in which the coil spring 52 forces the control vane 39 to a small damper opening position to permit a small amount of air to pass by the damper 34. This position, however, is reached near the end of the timing period in which the timer contacts 25 are closed and therefore only a slight amount of forced air is permitted to pass to the burning fuel to promote combustion.

During the operation of the stoker the volume of air passing the air damper and therefore generally a measure of the thickness and burning rate of the fuel may be readily perceived by observation of the point at which the indicator 6-! is positioned on the scale 68.

Referring now to the modification of the invention as disclosed in Fig. 6, the electric heater for the warp element 49 is here arranged so that it normally is energized with the stoker at rest and de-energized when the stoker operates. This is exactly the reverse condition which prevails from the arrangement of Fig. 3. The circuit for the heater 5| is arranged so that the line feed wires 20 and 2| are connected normally in series with the heater coil 5! and the stoker motor I3, so the heater is always normally energized. The electrical resistance of the heater 5!, however, is chosen so as to be sufiiciently high that the stoker motor I3 cannot operate with the heater in series with it. When there is a call for heat by the room thermostat the relay winding is energized, closing its contacts I9 and connecting the stoker motor l3 directly across the line Wires 20 and 21, while the heater 5| is short circuited by the contacts. As a result the bimetal warp element 49 gradually cools oif and moves its free end from the position shown in Fig. 6 to a position similar to that depicted in Fig. 5. The resulting action is effective to produce a gradual opening of the damper in the same manner as has been previously described and therefore need not be repeated at this point. When the call for heat has been satisfied the relay contacts are opened, thereby connecting the heater in series with the stoker motor to cause the motor to stop and permit the energization of the heater by removing the short circuit from it. The warp element 49 gradually assumes the position shown in Fig. 6 and effects the closing of the damper in the manner as has been explained.

Certain advantages are derivedfrom this arrangement. For example, should it occur that the electric heater became disabled for some reason, the control vane would still be permitted to function to open the damper and enable combustion air to pass to the fuel bed wheneve the stoker is operated. In case the heater is disabled during a period in which the stoker apparatus is at rest, the warp element 49 would gradually cool off and assume a position similar to that de-' picted in Fig. 5 and the damper would be slightly open. With this condition assumed the operation of the stoker at this time would feed fuel to the fuel bed and also enable a certain volume of air to flow past the damper to the fuel bed to promote combustion and also build up pressure in the air duct as the fuel bed resistance increases. While the blowing of fly ash through the retort is not entirely obviated by this arrangement since the initial flow of air is not altogether retarded, this is more desirable than having the damper held tightly closed by the disabling of the type of heater which is only energized when the stokeroperates, and thereby cause filling of the combustion chamber with unburned fuel. A further advantage in providing a normally energized heater is that a constant check upon its operativeness is provided.

From the foregoing disclosure it will be seen that a novel air damper control has been devised which may be readily installed upon existing or new stoker installations, which comprises relatively few parts, can be cheaply constructed and is reliable in operation. While only a preferred embodiment of the invention has been illustrated and described, it Will be understood that various changes and modifications in the same may be devised by those skilled in the art without departing from the invention, and it is therefore to be understood that the invention is not limited to the precise disclosure but only by the extent of the appended claims.

What is claimed is:

1. In an air damper control for stokers, conduit means through which combustion air is delivered and wherein static pressures are developed, an air damper for controllin the flow of 'air through the conduit means, a control member connected to said air damper for moving the same between open and closed positions in response to said static air pressures, a slow operating electrically actuated device, a coil spring connection extending between the control member and the slow operating device, said coil spring effective to be compressed by the energization of the slow operating device and tensioned by the de-energization of the device whereby the control member is controlled to delay movement of the air damper, and adjusting means for regulating the action of the coil spring.

2. In an air damper control for motor driven stokers, conduit means through which combustion air is delivered by the moto and wherein static air pressures are developed, a pivoted air damper controlling the air flow through the conduit means and having an operating member extending therefrom, a control member connected to said operating membe for moving said air damper between open and closed positions, a slow operating device having a flexible connection with said control member for delaying the opening of said air damper when the motor starts to deliver combustion air through the conduit means, said air damper having a larger portion extending from one side of its pivot than from the other side whereby the damper is unbalanced and held closed by the pressure of the air until the slow operating device is operated a predetermined extent, said flexible connection being effective at such time to move the control member against the force of the air pressure acting against the unbalanced portion of the dampe and thereby initiat opening movement of the damper.

3. In a stoker air damper control, an air duct through which combustion air is delivered and wherein air pressures are developed, an air damper in said air duct, a control vane connected to said air damper for moving the same between open and closed positions in response to pressure changes, a slow operating device, a first spring connected to said control vane, a second spring connecting the first spring with the slow operating device, said second spring being effective in the non-operated position of the slow operating device to stress the first spring in a direction to urge the control vane in damper closing direction and effective in an operated position of the slow operating device to stress the first spring in a direction to urge the control 'vane in damper opening direction, and means for preventing substantial flexing of said first spring when the second spring is urging the con. trol vane to close the damper while permitting said first spring to flex when the second spring is urging the control vane to damper opening position.

4. In an air damper control for a stoker fired furnace in which a stoker is arranged to feed fuel and deliver combustion'air to a burning fuel bed and in which varying pressures are developed as a result of varying thicknesses of the fuel bed, the combination of, air damper means for controlling the passage of air to the fuel bed, means responsive to the resistance of the fuel bed to airflow therethrough for positioning said damper means, said responsive means being constructed and arranged to move said damper means toward draft retarding position as the re sistance decreases and to move the damper means toward draft increasing position as the resistance increases, means responsive to the demand for heat from the stoker for starting and stopping the same, and means including a slow operating electrical device actuated as an incident to stopping of the stoker and operative to maintain the damper means in draft inducing position for a substantial period of time following stopping of the stoker, in order to provide a supply of air to the fuel bed by natural draft to consume the volatile constituents of the green coal therein, said slow operating electrical device acting after said period of time to effect movement of the damper means to draft retarding position.

5. In an air damper control for a stoker fired furnace in which a stoker is arranged to feed fuel and deliver combustion air to a burning fuel bed and in which varying pressures are developed as a result of varying thicknesses of the fuel bed, the combination of, air damper means for controlling the passage of air to the fuel bed, means responsive to the resistance of the fuel bed to air flow therethrough for positioning said damper means, said responsive means being constructed and arranged to move said damper means toward draft retarding position as the resistance decreases and to move the damper means toward draft increasing position as the resistance increases, means responsive to the demand for heat from the stoker for starting and stopping the same, and means including a thermostatic element which changes in temperature as an incident to stopping of the stoker for retaining said damper means in draft inducing position for a substantial period of time following stopping of the stoker, said thermostatic element after said period of time effecting movement of the damper means to draft retarding position.

6. In an air damper control for a stoker fired furnace in which a stoker is arranged to feed fuel and deliver combustion air to a burning fuel bed and in which varying pressures are developed as a result of varying thicknesses of the fuel bed, the combination of, air damper means for controlling the passage of air to the fuel bed, means responsive to the resistance of the fuel bed to air flow therethrough for positioning said damper means, said responsive means being constructed and arranged to move said damper means toward draft retarding position as the re sistance decreases and to move the damper means toward draft increasing position as the resistance increases, means responsive to the demand for heat from the stoker for starting and stopping the same, and means including a thermostatic element which changes in temperature as an incident to starting of the stoker for retaining thedamper means in draft retarding position for a period of time following starting of the stoker, said thermostatic element after said period of time causing the damper means to regulate the flow of air in accordance with the thickness of the fuel bed.

7. In an air damper control for a stoker fired furnace in which a stoker is arranged to feed fuel and deliver combustion air to a burning fuel bed and in which varying pressures are developed as a result of varying thicknesses of the fuel bed, the combination of, an air damper for controlling the passage of air to the fuel bed, a control means responsive to said pressures for operating said damper in accordance with the thickness of the fuel bed, a slow operating electrical device controlled with the stoker, a yieldable connection extending between the slow operating device and the damper control means, said. slow operating device being operative through said flexible connection to introduce a delay in the movement of the damper to flow increasing position by the control means and also being effective to slowly restore the damper to flow decreasing position upon the stopping of the stoker. 8. In an air damper control for a stoker fired furnace in which a stoker is arranged to feed fuel and to deliver combustion air to a burning fuel bed through conduit means and in which varying pressures are developed in the conduit means as a result of varying thicknesses of the fuel bed, the combination of, an air damper for controlling the flow of air through the conduit means, a control member arranged outside the conduit means and connected to the air damper, said control member operated by pressures in the conduit means to position the damper in accordance therewith, delay means for delaying movement of the damper to flow increasing position upon the initial operation of the stoker, said delay means comprising a slow operating electric device controlled with the stoker and operative to restore and maintain the control member in the position in which the damper assumes flow restricting position when the stoker is stopped and effective a period of time after starting of the stoker to urge the control member in a direction to increase the flow of air to the fuel bed. 9. In an air damper control for a stoker fired furnace in which a stoker is arranged to feed fuel and to deliver combustion air through conduit means to a burning fuel bed and in which varying pressures are developed in the conduit means as a result of varying thicknesses of the fuel bed, the combination of, damper means for controlling the flow of air through the conduit means, a control member connected to the damper means, a housin for said control member having an opening extending into said conduit means whereby the pressures in the conduit means are effective to actuate the control member to move the damper means to various positions in accordance with the static pressures, a slow operating electric device arranged within the housing and controlled with the stoker, a spring connection extending between the slow operating device and the control member, said spring connection being stressed normall to hold the control member in a position to maintain the damper means in flow restricting position, the stress being released upon the operation of the slow operating device, said spring connection being stressed oppositely upon the full operation of the slow operating device and effective to urge the control member in a direction to increase the flow of air to the fuel bed. 7

10. In an air damper control for stokers, conduit means through which combustion air is delivered and wherein static air pressures are developed, damper means for controlling the air flow through the conduit means, a housing outside said conduit means, a control member in the housing connected to the damper means for moving the same in response to the static pressures, said housing having an air opening therein extending into said conduit means to permit the static pressures to act upon the control member, a thermally actuated device in said housing, means for thermally insulating said device from the air in said conduit means, and means including the thermal device for interposing a delay in the control of the damper means by the control member.

11. In an air damper control for stokers, conduit means through which forced combustion air is delivered and wherein air pressures are developed, damper means for controlling the flow through the conduit means, a housing outside said conduit means, a control member in the housing connected to the damper means for moving the same in response to pressure changes, said housing having an opening therein extending into said conduit means, means including a partition in said housing cooperating with said control member to divide said housing into a first portion communicating with said conduit means and a second portion in which a different pressure exists than in the first portion, a thermally actuated device in said housing for influencing the control of the damper means by the control member, and a second partition in the housing for thermally isolating the thermally actuated device.

12. In an air damper control for stokers, conduit means through which combustion air is delivered and wherein static air pressures are developed, damper means for controllin the flow of air through the conduit means, a housing located outside said conduit means, a control member within said housing connected to said damper means for moving the same in response to pressure changes, said housing having an opening therein providing communication between the conduit means and the housing for applying air pressure to the control member, means including a thermally operated device in the housing for interposing a delay in the control of the damper means by the control member, a partition in the housing for thermally isolating the thermal device, said housing having a second opening there in extending to the outside of the housing to provide an escape port for the air on the other side of the control member, and means for adjusting the size of said escape port to regulate the operation of the control member.

13. In a control system for a stoker fired furnace having fuel feeding means and conducting means, damper means associated with said conducting means for influencing the furnace draft, means including a pressure responsive device separate from said damper means and responsive to a pressure condition in a portion of said conducting means for positioning said damper means in a manner tending to maintain proper combustion conditions, means responsive to the demand for heat from the furnace for starting and stopping the stoker, and means comprising a thermostatic element which changes in temperature upon starting or stopping of the stoker for controlling said damper means, said last recited means retaining the damper means in draft inducing position irrespective of said pressure for a substantial period of time following stopping of the stoker in order to provide a supply of air to the fuel by natural draft to consume the volatile constituents of green coal supplied to the fire, said thermostatic element acting after said period of time to effect movement of the damper means toward draft retarding position.

14. In a control system for a stoker fired furnace having fuel feeding means and conducting means, pressure responsive damper means associated with said conducting means for influencing the furnace draft, said damper means responding to only static pressure in said conducting means and being movable in draft retarding direction upon decrease in said static pressure, means responsive to the demand for heat from the furnace for starting and stopping the stoker, and means comprising a thermostatic element which changes in temperature upon starting or stopping of the stoker for controlling said damper means, said last recited means retaining the damper means in draft inducing position irrespective of said pressure for a substantial period of time following stopping of the stoker in order to provide a supplyof air to the fuel by natural draft to consume the volatile constituents of green coal supplied to the fire, said thermostatic element acting after said period of time to effect movement of the damper means to draft retarding position,

15. In an air damper control for a stoker fired furnace in which a stoker is arranged to feed fuel and deliver combustion air to a burning fuel bed,

the combination of, air damper means associated with the stoker for controlling the delivery of air to the fuel bed, said air damper means responding to pressure of the delivered air and regulating the delivery of air in accordance with such pressure, adjustable biasing means connected to the air damper means for biasing the same, means responsive to the demand for heat from the furnace for starting and stopping the stoker, and means comprising a thermostatic element which changes in temperature as an incident to starting or stopping of the stoker for adjusting said biasing means to maintain one value of bias when the stoker is in operation and to maintain another value of bias when the stoker is at rest.

16. In an air damper control for a stoker fired furnace in which a stoker is arranged to feed fuel and deliver combustion air to a burning fuel bed, the combination of, air damper means associated with the stoker for controlling the delivery of air to the fuel bed, a pressure responsive member for actuating said damper means and acting to move said damper means to draft inducing position upon increase in pressure applied to said member, means for applying air pressure produced by operation of the stoker to said pressure responsive member, means responsive to the demand for heat from the furnace for starting and stopping the stoker, a control device arranged to move from an initial position to a second position a period of time following starting of the stoker, and means controlled by said control device for preventing supply of air to the pressure responsive member when the control device is in its initial position while permitting air supply to said member when the control device moves to its sec- 0nd position.

' CLIFFORD HOTCHKISS. 

